[SeaBIOS] [PATCH v2 1/2] Add QEMU fw_cfg DMA interface

[Marc Marí]

Add support for the new fw_cfg DMA interface. The protocol is explained in
QEMU documentation.

Signed-off-by: Marc Marí 
---
 src/fw/paravirt.c | 65 ++++++++++++++++++++++++++++++++++++++++++++++++++++---
 src/fw/paravirt.h | 25 +++++++++++++++++----
 2 files changed, 83 insertions(+), 7 deletions(-)

diff --git a/src/fw/paravirt.c b/src/fw/paravirt.c
index db22ae8..26af499 100644
--- a/src/fw/paravirt.c
+++ b/src/fw/paravirt.c
@@ -23,6 +23,7 @@
 #include "util.h" // pci_setup
 #include "x86.h" // cpuid
 #include "xen.h" // xen_biostable_setup
+#include "stacks.h" // yield

// Amount of continuous ram under 4Gig
 u32 RamSize;
@@ -30,6 +31,13 @@ u32 RamSize;
 u64 RamSizeOver4G;
 // Type of emulator platform.
 int PlatformRunningOn VARFSEG;
+// cfg_dma enabled
+int cfg_dma_enabled = 0;
+
+inline int qemu_cfg_dma_enabled(void)
+{
+    return cfg_dma_enabled;
+}

/* This CPUID returns the signature 'KVMKVMKVM' in ebx, ecx, and edx.  It
  * should be used to determine that a VM is running under KVM.
@@ -199,16 +207,57 @@ qemu_cfg_select(u16 f)
 }

static void
+qemu_cfg_dma_transfer(u64 address, u32 length, u32 control)
+{
+    QemuCfgDmaAccess access;
+    void *p = &access;
+
+    *(u64 *)(p + offsetof(QemuCfgDmaAccess, address)) =
+                                        cpu_to_be64(address);
+    *(u32 *)(p + offsetof(QemuCfgDmaAccess, length)) =
+                                        cpu_to_be32(length);
+    *(u32 *)(p + offsetof(QemuCfgDmaAccess, control)) =
+                                        cpu_to_be32(control);
+
+    barrier();
+
+    outl((u32)p, PORT_QEMU_CFG_DMA_ADDR_LOW);
+
+    u32 len;
+    u32 ctl;
+
+    do {
+        yield();
+        len = be32_to_cpu(*(u32 *)(p +
+                offsetof(QemuCfgDmaAccess, length)));
+        ctl = be32_to_cpu(*(u32 *)(p +
+                offsetof(QemuCfgDmaAccess, control)));
+    } while(len != 0 && !(ctl & QEMU_CFG_DMA_CTL_ERROR));
+}
+
+static void
 qemu_cfg_read(void *buf, int len)
 {
-    insb(PORT_QEMU_CFG_DATA, buf, len);
+    if (qemu_cfg_dma_enabled()) {
+        qemu_cfg_dma_transfer((u64)(u32)buf, len, QEMU_CFG_DMA_CTL_READ);
+    } else {
+        insb(PORT_QEMU_CFG_DATA, buf, len);
+    }
 }

static void
 qemu_cfg_skip(int len)
 {
-    while (len--)
-        inb(PORT_QEMU_CFG_DATA);
+    if (len == 0) {
+        return;
+    }
+
+    if (qemu_cfg_dma_enabled()) {
+        qemu_cfg_dma_transfer(0, len, QEMU_CFG_DMA_CTL_SKIP);
+    } else {
+        while (len--)
+            inb(PORT_QEMU_CFG_DATA);
+    }
 }

static void
@@ -422,8 +471,18 @@ void qemu_cfg_init(void)
     for (i = 0; i < 4; i++)
         if (inb(PORT_QEMU_CFG_DATA) != sig[i])
             return;
+
     dprintf(1, "Found QEMU fw_cfg\n");

+    // Detect DMA interface.
+    u32 id;
+    qemu_cfg_read_entry(&id, QEMU_CFG_ID, sizeof(id));
+
+    if (id & QEMU_CFG_VERSION_DMA) {
+        dprintf(1, "QEMU fw_cfg DMA interface supported\n");
+        cfg_dma_enabled = 1;
+    }
+
     // Populate romfiles for legacy fw_cfg entries
     qemu_cfg_legacy();

diff --git a/src/fw/paravirt.h b/src/fw/paravirt.h
index 95ffb92..5e5c61e 100644
--- a/src/fw/paravirt.h
+++ b/src/fw/paravirt.h
@@ -9,6 +9,12 @@
 #define PF_XEN      (1<<1)
 #define PF_KVM      (1<<2)

+typedef struct QemuCfgDmaAccess {
+    u32 control;
+    u32 length;
+    u64 address;
+} PACKED QemuCfgDmaAccess;
+
 extern u32 RamSize;
 extern u64 RamSizeOver4G;
 extern int PlatformRunningOn;
@@ -25,11 +31,22 @@ static inline int runningOnKVM(void) {
 }

// Common paravirt ports.
-#define PORT_SMI_CMD           0x00b2
-#define PORT_SMI_STATUS        0x00b3
-#define PORT_QEMU_CFG_CTL      0x0510
-#define PORT_QEMU_CFG_DATA     0x0511
+#define PORT_SMI_CMD                0x00b2
+#define PORT_SMI_STATUS             0x00b3
+#define PORT_QEMU_CFG_CTL           0x0510
+#define PORT_QEMU_CFG_DATA          0x0511
+#define PORT_QEMU_CFG_DMA_ADDR_LOW  0x0514
+#define PORT_QEMU_CFG_DMA_ADDR_HIGH 0x0518
+
+// QEMU_CFG_DMA_CONTROL bits
+#define QEMU_CFG_DMA_CTL_ERROR   0x01
+#define QEMU_CFG_DMA_CTL_READ    0x02
+#define QEMU_CFG_DMA_CTL_SKIP    0x04
+
+// QEMU_CFG_DMA ID bit
+#define QEMU_CFG_VERSION_DMA    2

+int qemu_cfg_dma_enabled(void);
 void qemu_preinit(void);
 void qemu_platform_setup(void);
 void qemu_cfg_init(void);